The present invention relates generally to exhaust systems for aircraft gas turbine engines, and in particular to a control system for selectively adjusting effective flow areas of an aircraft engine exhaust nozzle to change operational characteristics of the nozzle.
High performance advanced aircraft must operate over a wide range of flight conditions while maintaining good fuel efficiency and high maneuverability. Typically, these aircraft include an exhaust nozzle for each engine that permits variation in exhaust gas flow area. The nozzle has a convergent duct, a plane of minimum flow area known as a throat, and a divergent duct ending at a nozzle exit. The throat and exit may be varied in size to provide for efficient engine operation at all engine power settings, flight speeds, and altitudes. Some variable-area nozzles provide for controllable deflection of the direction of exhaust gas flow, known as thrust vectoring, to enhance aircraft controllability. Thrust vectoring offers the potential of substantial performance benefits and can permit conventional aerodynamic controls, such as tail surfaces, to be reduced in size or eliminated altogether.
Unfortunately, a variable-area nozzle requires a complex mechanism that is heavy and costly. It has several moveable flaps with associated linkages and hydraulic actuators. The mechanism adds weight and structural complexity, and requires regular maintenance. Even greater structural weight penalties are incurred to include the variable-area mechanism in nozzles having unconventional shapes, such as wide aspect ratio, elliptical, or diamond. Further, each moveable flap of the variable-area nozzle has edges and surface gaps between adjacent structure that can make the nozzle more visible on radar, which is undesirable for military aircraft.
As an alternative to mechanized variation of the physical boundaries of the throat and exit, the flow areas can be varied fluidically, thereby providing several advantages. Effective flow areas in a fluidic nozzle are varied by injecting pressurized air at selected locations along a perimeter of the throat or the divergent duct to constrict area available for exhaust gas, aerodynamically blocking a portion of the flow area. As a result, the nozzle can be mechanically fixed in geometry, without need for any moveable flaps. Nozzle weight is low because there are no actuators or moving parts, and the structure is more efficient. The nozzle may have any desired shape and is therefore more easily integrated into a structural design of an aircraft. Surfaces of the nozzle are smooth, without any gaps, permitting improved radar signature.
A drawback to the fluidic nozzle has been that a complex system of pipes, manifolds, and valves was needed to distribute pressurized air to desired locations. For instance, one type of fluidic nozzle requires three manifolds and nine valves, along with interconnecting pipes to deliver compressor discharge air to various locations. These parts add weight and cost and degrade reliability. Further, the parts must be dispersed about the nozzle and cannot be packaged into one location that is designed for reduced vulnerability to weapons, thus degrading survivability.
In general, a control system of the present invention selectively adjusts effective flow areas of an aircraft engine exhaust nozzle to change operational characteristics of the nozzle. The control system comprises a chamber having a hollow interior, a plurality of outlet passages extending from the hollow interior of the chamber to sites within the exhaust nozzle, and an adjustable inlet. The inlet extends from a pressurized air source to the hollow interior of the chamber for delivering a jet of pressurized air to the chamber. The inlet is adjustable to direct pressurized air to selected one or more outlet passages of the plurality of outlet passages for the delivery of air via the one or more outlets to corresponding one or more sites within the exhaust nozzle, thereby to change the operational characteristics of the nozzle.
In another aspect, a gas turbine engine of the present invention for providing propulsion to an aircraft has a fluidic control system. The engine comprises a nozzle having a duct for exhausting gas from the engine, the duct having at least one variable flow area for controlling operational characteristics of the engine. A source of pressurized air and a fluidic control system are included for selectively adjusting at least one flow area of the duct. The control system comprises a chamber having a hollow interior, a plurality of outlet passages extending from the hollow interior of the chamber to sites within the nozzle, and an adjustable inlet extending from the pressurized air source to the hollow interior of the chamber for delivering a jet of pressurized air to the chamber. The inlet is adjustable to direct pressurized air to selected one or more outlet passages of the plurality of outlet passages for the delivery of air via the one or more outlets to corresponding one or more sites within the nozzle thereby to change the operational characteristics of the engine.
In yet another aspect, a method of the present invention of selectively adjusting effective flow areas of an aircraft engine exhaust nozzle changes operational characteristics of the nozzle. The method comprises the steps of supplying pressurized air to a chamber having a hollow interior and a plurality of outlet passages extending from the hollow interior of the chamber to sites within the exhaust nozzle. At least a portion of the pressurized air is selectively directed toward at least one outlet passage of the plurality of outlet passages for delivery of the portion of air to a corresponding site within the exhaust nozzle to change the operational characteristics of the nozzle.
In still another aspect, a method of the present invention controls an aircraft engine exhaust nozzle of the type having fluidic injection capability whereby a first flow of pressurized gas is delivered to the nozzle and injected into an exhaust stream for fluidically varying operational characteristics of the nozzle. The method comprises the step of selectively controlling the injection of the first flow into the exhaust stream using a control system that is fluidic.
Other features of the present invention will be in part apparent and in part pointed out hereinafter.